Sensors of the above-mentioned type may be mounted to the patient's skin surface by means of a mounting device, which in turn is adhered to the skin surface. The mounting device may comprise a ring-shaped member that extends upwardly from the skin surface and includes a fastener for securing the sensor thereto. When the sensor is secured to the mounting device, a measuring chamber is defined by an inner surface of the mounting device, the skin surface, and a lower surface of the sensor. Following application of the mounting device to the skin surface, but prior to mounting of the sensor in the mounting device, drops of contact gel or liquid may be applied to the skin surface so that the liquid essentially fills the measuring chamber once the sensor has been mounted to the mounting device. As gases, such as oxygen and/or carbon dioxide, diffuse through the skin surface, the partial pressures of these gases in the measuring chamber become representative of the arterial and/or dermatologic partial gas pressures.
Recent development activities have aimed at reducing the dimensions of the sensor and the mounting device. However, as dimensions reduce, the sensors become more vulnerable to mechanical impact due to, e.g., movements of parts of patients' bodies. In particular, tests have shown that atmospheric air entering the measuring chamber may influence the partial gas pressures of e.g. oxygen and carbon dioxide in the measuring chamber to such an extent that measurements become non-representative of the arterial partial gas pressures.